In a variable displacement hydraulic pump/motor in which a displacement is changed by changing a tilt angle of a swash plate, a swash plate is supported in a casing by a pair of supports so as to be able to tilt, in general. Each of the supports is a circular columnar shaft portion having a tip end provided with a spherical sliding protruding portion. The two supports are mounted at the shaft portions thereof into mounting holes so that a line connecting centers of the spheres of the sliding protruding portions extends along a direction perpendicular to an axial center of a rotating shaft supporting a cylinder block. On the other hand, sliding recessed portions in which the sliding protruding portions are to be fitted are formed in the swash plate and the sliding protruding portions of the supports are respectively fitted for sliding in the respective sliding recessed portions.
In the hydraulic pump/motor, if the tilt angle of the swash plate is changed with respect to the axial center of the rotating shaft, stroke movement amounts of pistons disposed in cylinders in the cylinder block change according to the tilt angle of the swash plate and the displacement of the hydraulic pump/motor changes.
In this type of hydraulic pump/motor, oil is supplied between the sliding protruding portions of the supports and the sliding recessed portions in the swash plate from a port on a high-pressure side, i.e., a port for discharging the oil in a case of the hydraulic pump and a port to which the oil is supplied in a case of the hydraulic motor to carry out lubrication to thereby prevent problems such as seizing and galling from occurring (see Patent Literature 1, for example).